(1) Field of the Invention.
The present invention relates to tandem axle suspension systems for vehicles, in particular an asymmetric tandem axle suspension system for vehicles having single axle drive, where the suspension system distributes a majority of the tandem axle vehicle load to the drive axle.
(2) Description of the Related Art.
Tandem axle suspension systems of the type provided by the present invention commonly comprise a hanger member, a compensator assembled to the hanger member, and front and rear torque beams assembled to the compensator. These complete assembles are provided on opposite sides of the vehicle. Each hanger member is connected to and depends from a chassis member on opposite sides of the vehicle. A trunnion shaft extends laterally beneath the chassis of the vehicle and is supported by both hanger members on the opposite sides of the vehicle chassis.
A compensator member is pivotally mounted on the ends of the trunnion shaft, outboard from the hanger members. Each compensator member generally extends parallel to the longitudinal axis of the vehicle chassis, and only a short distance forward of and rearward of the adjacent hanger member. The compensator is also generally symmetric, having similar halves on opposite sides of a vertical plane extending through the pivot connection of the compensator to the trunnion shaft.
The front and rear torque beams are supported by the compensator member. One end of the front torque beam is pivotally connected to the compensator member, just forward of and below the pivot connection of the compensator member to the trunnion shaft. The front torque beam extends forward from its pivot connection to the compensator member and is pivotally connected to a front axle seat member at its forward second end. The front axle seat member generally supports a first drive axle of the vehicle. A torque rod is pivotally connected between the drive axle and the vehicle chassis to control the orientation of the drive axle relative to the vehicle chassis as the axle moves vertically when the vehicle is driven over a road. One end of the rear torque beam is also pivotally connected to the compensator member just rearward of and below the pivot connection of the compensator member to the trunnion shaft. The rear torque beam extends rearward from its pivot connection to the compensator member and is pivotally connected to a rear axle seat member at its rearward second end. The rear axle seat member also generally supports a second drive axle of the vehicle. A second torque rod is pivotally connected between the second drive axle and the vehicle chassis to control the orientation of the second drive axle relative to the vehicle chassis as the axle moves vertically when the vehicle is driven over a road.
Springs are positioned between both the front and rear torque beams and the compensator member to prevent the vertical movements of the first and second axles produced when the vehicle is driven over a road from being transmitted to the vehicle chassis.
In operation, as the tandem axle vehicle is driven over an uneven road surface, the torque beams supporting the axle seats oscillate vertically about their pivot connections to the compensator member. The oscillations of the torque beam exerts a compressive force on the springs positioned between the torque beams and the opposite ends of the compensator member. A fraction of this force is transmitted to the opposite ends of the compensator member, and causes the compensator member to pivot about its trunnion shaft connection and equalize the load distribution between the first and second axles of the tandem axle vehicle. This type of suspension system distributes the vehicle load substantially equally over the first and second drive axles of the vehicle, and the even distribution of the load equally enhances the traction of the vehicle wheels driven by the first and second drive axles.
This type of suspension system can also be used with tandem axle vehicles where only one of the two axles is a drive axle. However, because the compensator evenly distributes the vehicle load over both the drive axle and the drag axle, only about half of the vehicle load is transmitted to the vehicle wheels driven by the drive axle to enhance the traction of those wheels. The other half of the vehicle load is transmitted to the drag axle, but because this is not a drive axle it has no effect on increasing the traction of the vehicle.
The present invention solves this problem by providing an asymmetric tandem axle vehicle suspension system that distributes the vehicle load unevenly to the front and rear axles of a tandem axle vehicle. The asymmetric tandem axle suspension system of the invention can be used with vehicles having dual drive axles, but when used with tandem axle vehicles with only a single drive axle, it distributes a majority of the vehicle load to the drive axle, thereby enhancing the traction of the wheels driven by the drive axle over that which was obtainable by tandem axle suspension systems of the prior art.
It is therefore an object of the present invention to provide an asymmetric tandem axle vehicle suspension system that, when used with a tandem axle vehicle having only one drive axle, distributes a majority of the vehicle load to the drive axle, thereby increasing the tractive force of the vehicle wheels driven by the drive axle over that produced by single axle drive, tandem axle suspension systems of the prior art.